Electrophotographic printing is achieved by a process which includes creating a latent image by exposing a uniformly charged photoconductive member to a light source containing the information to be preserved; developing the latent image thus created; and transferring the developed image onto a suitable medium such as paper to form the hard copy. In an electrophotographic copier, the information is obtained by focusing the light reflected from the surface of a printed page, or other original, onto the photoconductive member. In an electrophotographic printer, a modulated light source scans the surface of the photoconductive member.
Many printers currently on the market are essentially copiers in which the optics associated with the imaging portion of the copier has been replaced with the much smaller light-scanning apparatus. In such cases, the paper path tends to follow a rather serpentine path from the paper source tray, under the optical imaging region of the original copier engine, and then up the other side of the machine to the output tray. This is not a problem so long as the machine operates properly. It is a problem, however, when there is a paper jam and layer upon layer of apparatus must be peeled away to reach the portion of the paper path along which the jam has occurred.
It is, therefore, a first object of the present invention to simplify the paper path in electrophotographic printers.
Another inconvenience typical of prior art printers is that the image is transferred to the top surface of the hard copy material. As a result, as the copies are deposited in the output tray they accumulate in reverse order, with the last page on top and the first page on the bottom of the stack. Thus, each series of pages must then be collated either by hand or by means of additional apparatus.
It is, accordingly, a second object of the present invention to print copies such that collation occurs automatically.
Having established the ability to collate, various printing tasks can be simplified. For example, it would be convenient to be able to run off many copies of the same, multiple page report, or copies of different, multiple page reports. Inasmuch as each is collated in the manner described hereinabove, the several reports should be readily available for distribution. However, if the conventional output tray is used, a number of difficulties are encountered. For example, as the copies deposited on the output tray build up, a point is reached where subsequent copies are no longer deposited properly. This would limit the number of copies that could be made before the tray required emptying. A second problem resides in the fact that there is no convenient way of determining where one report ends and the next report begins. Thus, the stack would have to be examined, page by page, in order to separate successive copies of reports.
Thus, it is a further object of the invention to provide a means whereby more copies can be made before the output tray must be emptied and, in addition, to provide means for distinguishing between selected groups of copies.